In a charged particle beam apparatus typified by a scanning electron microscope (hereinafter, referred to as an SEM) and a scanning transmission electron microscope (hereinafter, referred to as an STEM), an aberration corrector has been incorporated in order to improve the resolution. The aberration corrector is configured with plural stages of multipole lenses and generates an electric field or a magnetic field to eliminate aberration contained in a charged particle beam passing through the interior thereof by using the multipole lenses. NPL 1 discloses an aberration corrector using four stages of multipole lenses.
In addition, generally, in order to correct aberrations in an arbitrary direction, a line cross (a function of only a convex lens in a specific direction and a function of a concave lens in a direction perpendicular to the specific direction) is formed in directions where the incident charged particle beams are perpendicular at different positions in the traveling direction, negative aberration is generated independently of each perpendicular direction and is applied to the charged particle beam passing through an aberration corrector. Hereinafter, the direction of the convex lens is referred to as a line cross direction, and the direction of the concave lens is referred to as a line cross parallel direction.
Furthermore, since it is required that there is no anisotropy in the aperture angle and the optical magnification of the electron beam on the sample surface after the aberration correction for the convenience of application, in general, the corrector is designed so that the above condition is satisfied when the line cross is formed at the center of the traveling direction (hereinafter, referred to as a z direction) of the charged particle beams of the second-stage and third-stage multipoles. In addition, in the aberration correction, as disclosed in PTL 1, the trajectory of the charged particle beam is constructed so that a line cross is formed in the perpendicular directions at the center position of the z-direction the second-stage and third-stage multipoles. More specifically, by using a deflector configured with second-stage and third-stage multipoles for the corrector, the intensities of the quadrupole fields of the first stage and the second stage are adjusted so that all the deflection sensitivities in the line cross direction becomes sufficiently small, and thus, the line cross position is aligned the with the center position in the z direction of the poles of the second stage and third stage, so that the trajectory for aberration correction is constructed.